/Engine/Source/Runtime/RenderCore/Public/UnifiedBuffer.h
Init with presized num scatters, expecting each to be set at a later point. Requires the user to keep track of the offsets to use.
void InitPreSized ( [FRDGBuilder](API\Runtime\RenderCore\FRDGBuilder) & GraphBuilder, uint32 NumElements, uint32 InNumBytesPerElement, bool bInFloat4Buffer, const TCHAR * DebugName )